Technical Field
The disclosure relates to a variable nozzle for an aeronautic gas turbine engine and in particular relates to a variable nozzle capable of reducing loss in thrust thereof.
Description of the Related Art
An exhaust nozzle of an aeronautic gas turbine engine has a function of rectifying and ejecting exhaust gas rearward and, as well, a function of regulating its flow velocity. In a case where the gas turbine engine is operated only within a subsonic speed range, usually used is a so-called convergent nozzle that converges toward the downstream direction in order to increase the velocity of the exhaust gas flow. In a case where the gas turbine engine is also operated beyond the sonic speed, frequently used is a so-called convergent-divergent nozzle that once converges the exhaust gas flow and thereafter, downstream of a throat, expands the flow. A convergent-divergent nozzle may be constructed as a variable nozzle that variates the aperture areas of the throat and the exhaust exit respectively in order to optimize its efficiency over a wide range of speed. The literatures listed below disclose related arts of variable nozzles.
Japanese Patent Application Laid-open No. H05-141310
Japanese Patent Application Laid-open No. S54-19004
Japanese Patent Application Laid-open No. H04-334749
Japanese Patent Application Laid-open No. H03-100359
Variable nozzles require extremely high thermal resistance as they are directly exposed to high-temperature exhaust gas. Materials that can meet such a requirement of thermal resistance are, in general, poorly workable and are therefore available only for producing members with simple shapes such as flat panels. Thus, generally, a plurality of flaps and a plurality of seals, respectively formed into flat shapes, are combined to produce a variable nozzle. Experts frequently carry out numerical analysis of flow fields of exhaust gas to determine ideal flow path shapes and then determine dimensions and arrangement of flat flaps and flat seals so as to approximate these ideal flow path shapes.